CN109854220B - Liquid injection pipe sealing method suitable for low-permeability reservoir hydraulic fracturing simulation test - Google Patents

Abstract

The invention provides a liquid injection pipe sealing method suitable for the hydraulic fracturing simulation test of low-permeability reservoirs. The glue-making adhesives A and B liquids are used, and dodecyl to tetradecyl glycidyl ether and ethanol are used as sealing materials. ; When injecting glue, it is sealed by multiple injections, and it is slowly injected in 8-10 layers, and the injection interval of each layer is 9-10s. Affect the injection of the naked eye segment. The invention eliminates the leakage problem of the sealed pipe section in the hydraulic fracturing process, enables the fracturing fluid to reach the target area smoothly through the liquid injection pipe, has strong operability, and can effectively solve the sealing problem of leakage at the rock-glue interface. The fracturing test is of great significance.

Description

A liquid injection pipe sealing method suitable for hydraulic fracturing simulation test of low permeability reservoir

technical field

The invention belongs to the field of laboratory testing and unconventional energy development, in particular to a sealing method suitable for a low-permeability rock sample hydraulic fracturing liquid injection pipe.

Background technique

At present, in the field of unconventional energy, the exploitation of tight gas reservoirs has become a hot topic. According to the geological conditions, the reservoirs will be reformed when exploiting low-permeability gas. Hydraulic fracturing is the main method. Due to various reasons on the site, it is impossible to ideally analyze the effect of the reconstruction. At present, researchers mainly rely on indoor experimental instruments to physically simulate the process of on-site fracturing and reconstruction. Production provides strong theoretical support. In addition, when the hydraulic fracturing test is performed, whether it is the reshaped sample or the original sample, it is necessary to consider the sealing problem of the rock sample and the liquid injection pipe during the hydraulic fracturing process. Therefore, it is very important to study the sealing problem of the bonding between the two. Promoting the further development of hydraulic fracturing test can also further guide the actual mining on site. In recent years, with the gradual deepening of the research on unconventional energy drilling and mining represented by shale gas and coalbed methane, related laboratory experiments have been carried out one after another. After research, it is found that the sealing treatment of rock samples to simulate wellbore exists

(1) The injection pipe and the rock sample are simply connected, and the effect and strength of the seal are not considered, so that the leakage of the sealing section occurs before the crack initiation pressure of the rock sample is reached;

(2) There is no good protection for the naked eye segment, and the colloid may penetrate into the naked eye segment to block the injection hole;

(3) Interfering factors such as air bubbles will be generated in the conventional one-shot glue injection process.

Based on the above shortcomings, some researchers put the liquid injection tube in the predetermined position of the sample to be processed during the preparation of the sample, and formed it together with the sample, but it is suitable for very few sample types. , and no open-hole section can be reserved, so the above deficiencies are improved, the colloid is prepared, the end of the liquid injection pipe is processed, the liquid injection operation is adjusted, and the glue is injected in layers, and it is proved that the rock-glue formed under this glue injection method is stronger. Therefore, the rock samples can be better bonded to the liquid injection pipe, so that the effect of hydraulic fracturing test is better, and it is of great significance for the development of laboratory simulation test of hydraulic fracturing in unconventional energy reservoirs.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a low-permeability sample liquid injection pipe sealing method suitable for hydraulic fracturing, aiming at the deficiencies in the sealing process of the sample liquid injection pipe in the hydraulic fracturing test.

In order to achieve the above object, technical scheme of the present invention is as follows:

A sealing method for a low-permeability rock sample liquid injection pipe suitable for indoor hydraulic fracturing, which is characterized by comprising the following steps:

Step S1, drilling: at the injection site, drill the diversion hole along the injection direction to a depth of 3/5-2/3 of the length of the sample, and remove debris;

Step S2, prepare colloid: respectively measure 40%-45% of the total colloid volume of A glue and 40%-45% of the total colloid volume of 40% to 45% of the B glue, mix them according to the ratio of A glue:B glue to 1:1, and then measure them separately. Take dodecyl to tetradecyl glycidyl ether at 9%-17% of the total colloid volume and mix with ethanol at 1%-3% of the total colloid volume as a diluent and add it to the mixed AB glue to slow down the initial setting time of the colloid. Strengthen the sealing effect;

Step S3, treatment of the end of the liquid injection pipe: cover the elastic sealing ring at a distance of 5-10mm from the bottom of the liquid injection pipe, press it with sealing tape, and fix the elastic sealing ring and the liquid injection pipe;

Step S4, fix the liquid injection pipe: extend the processed liquid injection pipe into the place of 1/2-2/3 of the drilling depth and fix it, and reserve the open hole section;

Step S5, glue injection: insert the glue injection needle tube into the bottom of the annular space between the sample and the liquid injection tube, initially inject a small amount of colloid (1/50 volume of the colloid) to the sealed end to form the initial setting interface, and then divide the colloid into the smallest amount. 8 parts are injected into the sealing section, and the interval between each injection is 9-10s, and ensure that each injection needle is kept in the gel to complete the sealing.

Further, the mixing volume of the A and B glues is preferably 80%-85% of the drilling volume, the consolidation strength of the colloid must be greater than the crack initiation strength of the rock sample, and the initial setting time is greater than 20 minutes, and the final colloid is reached in 24 hours. Consolidation strength.

Further, the diluent can reduce the viscosity of the colloid and participate in the curing reaction, wherein the volume of dodecyl to tetradecyl glycidyl ether is preferably 9%-17% of the volume of the colloid, and the best ethanol is 2%.

Further, the sealing ring is a fluororubber O-ring, which is tightly clamped to the liquid injection pipe, and has elasticity, high temperature resistance, acid and alkali resistance, and corrosion resistance.

Further, the fixed position of the sealing ring is preferably 5 mm from the bottom of the liquid injection pipe, and the distance between the bottom of the liquid injection pipe and the bottom of the drilling hole is preferably 1/3 of the depth of the drilling hole.

Further, the amount of the first injection is as small as possible, but the thickness of the glue should cover at least 3mm above the sealing end, and the number of injections is adjusted according to the length of the injection tube, generally more than 8 times. temperature remains the same.

The present invention adopts multiple injections. Compared with the single injection currently used, multiple injections have obvious advantages. The mechanism is as follows:

Take the interface between the colloid and the rock sample for analysis: it is assumed that the sealing ring and the sealing tape are closely combined, the mass is small, and the friction force with the rock sample is enough to bear the weight of the colloid; the rock sample and the colloid are homogeneous; the single injection time extremely short; the colloid medium is uniform, and the heat dissipation rate of the rock-cement interface is the same; the initial temperature of colloid injection is T ₀ , the temperature of colloid and rock sample cementation is at least greater than T _c , and when the temperature is greater than T _c , the average rate of cement formation is

可知，一定的热量在不同的介质传播速率不同，注入胶体后，胶体下端与弹性密封圈、密封胶带接触，传热快，温度由T₀降到T_c用时短，为

上部与空气接触，传热慢，温度由T₀降为T_C用时长，为

中间部分胶结时间为t_中部，因此在底端和顶端存在区别于中间部分的不均匀胶结区，底端不均匀区胶结深度与距底端距离的函数为H_下(l)；上端胶结深度与距中间部分上端距离的函数为H_上(l)。From the above, the thickness of the cement formed by injecting a unit thickness of colloid is determined by the time when the temperature drops from T ₀ to T _c , according to

It can be seen that a certain amount of heat spreads at different rates in different media. After the colloid is injected, the lower end of the colloid contacts the elastic sealing ring and the sealing tape, the heat transfer is fast, and the temperature is reduced from T ₀ to T _c in a short time, which is

The upper part is in contact with the air, the heat transfer is slow, and the time required for the temperature to drop from T ₀ to T _C is

The cementation time _of the middle part is the _middle of t, so there are uneven cementation areas at the bottom and top that are different from those in the middle. The function of _the distance from the upper end of the middle section is Hup(l).

分别表示空气、岩样、注液管、胶体、密封圈的导热系数。Among them, u=u(t,x,y,z) represents the temperature, which is a function of time t and space (x,y,z), k is the thermal diffusivity of the colloid,

Indicates the thermal conductivity of air, rock sample, liquid injection pipe, colloid, and sealing ring, respectively.

If the glue is injected in multiple times, after the Nth (N≠1) injection, the ratio of the length l _N1 of the uneven area at the bottom end to the total length l _N of the glue injection is l _N1 /L _N =m, and the length of the uneven area at the upper end is l N1 /L N =m The ratio of the length l _N3 to the total length l _N of the glue injection l _N3 /L _N =n, ignoring other unnecessary factors, except for the first glue injection, l _N1 /L _N =m, l _N3 /L _N =n is Value. Due to the heat diffusion of the temperature difference, a uniform cement body is finally formed at the contact ends of two adjacent glue injections.

The first glue injection length l ₁ is 1/k of the total glue injection length L, and the bonding area is:

即在满足完全覆盖密封段端部的前提下，首次注入较少的胶体量为宜，第一次注胶后端部不均匀区域的长度l₁₁与第一次注胶的总长l₁的比值l₁₁/l₁＝m₁，上端不均匀区域的长度l₁₃与第一次注胶的总长l₁的比值l₁₃/l₁＝n₁。When k→+∞,

That is, under the premise of completely covering the end of the sealing section, it is appropriate to inject a small amount of colloid for the first time, and the ratio of the length l11 of the uneven area at the rear end of the first glue injection to the total length _l1 of the _first glue injection l ₁₁ /l ₁ =m ₁ , and the ratio l ₁₃ /l ₁ =n ₁ of the length l ₁₃ of the uneven region at the upper end to the total length l ₁ of the first glue injection.

Bonding area after N injections:

上式仅k和N为未知参数。When (k→∞∩N→∞), the corresponding bonding area after N injections is

In the above formula, only k and N are unknown parameters.

If the cemented area is injected all at once:

It can be known that: s _{one injection} < s _total <s' _total

It can be seen from the above that the area of cement formed by multiple injections is larger than that formed by one injection, so the problem of injection of rock seals needs to be reduced from T ₀ to T _c by analyzing the combination rate and temperature of colloid and rock samples. Determine the glue injection time interval; consider the size of the rock sample drilling diameter, the first glue injection amount and the glue injection times can be adjusted; if the sealing material is changed, n can be adjusted, and m can be adjusted in different air environments , to maximize the strength of the bonding interface, so as to solve the problem of rock sample sealing, that is, under the condition of a certain sealing material, control the amount of initial glue injection and the number of cumulative glue injections, and achieve uniform glue injection within a certain time interval. Uniform area, so that the bond interface strength is improved.

Therefore, according to the rock samples and sealing materials, the injection temperature of the mixed colloid is set to 80 °C, the first injection volume is 1/50 of the total volume of glue, and then the colloid is injected in 8-10 layers, and the injection interval Δt is less than that of the rock. The consolidation time of the sample and the colloid was determined to be 9-10s. Analysis of the stress on the cement interface during fracturing: the stress (3σ _{circumference} - σ _axis - σ _t ) acting on the bottom end of the cement interface by the fracturing fluid, the strength of the colloid combined with the rock sample is σ _{gel - rock} , through the above operation colloid strength Satisfy:

Compared with the prior art, the sealing method of the present invention has the following advantages:

(1) The colloid can maintain its fluidity within 20 minutes by mixing with dodecyl to tetradecyl glycidyl ether and ethanol, which is beneficial to the sealing of the injection pipe of hydraulic fracturing, and the sealing effect required by the sample can be achieved within 24 hours. .

(2) The end of the liquid injection pipe, that is, 5mm from the bottom of the liquid injection pipe, is sealed and isolated with a sealing ring and sealing tape. The colloid enters the open-hole segment to block the injection hole.

(3) By optimizing the amount of the first injection and using multiple injections, the sealing layer of the colloid can be made more uniform and the bonding strength is improved. The invention adopts the mixed colloid formula and injects into 8-10 layers at a time interval of 9-10S, so as to achieve better cementation strength and meet the requirements of rock sample crack initiation pressure. The method has strong operability, and the target samples are low-permeability, dense hard brittle rock samples or reshaped samples, which improves the effect of hydraulic fracturing simulation test.

Description of drawings

The drawings described herein are used to provide further understanding of the embodiments of the present application, and constitute a part of the embodiments of the present application, and do not constitute limitations to the embodiments of the present application.

Fig. 1 is the front view of the sealing simulation result of the liquid injection pipe of the application;

Fig. 2 is the C-C sectional view in Fig. 1;

Figure 3 is an internal view of the sample after hydraulic fracturing;

Figure 4 is a graph of the water pressure of the sealing sample.

Detailed ways

In order to make the purposes, technical solutions and advantages of the embodiments of the present application more clearly understood, the present invention will be further described below in conjunction with the embodiments. limited.

Example 1

The sealing method of the liquid injection pipe of the present invention is illustrated by the sealing of the liquid injection pipe of the cylindrical rock sample, as shown in FIG. 1 .

Step S1. Drilling: at the center of the upper surface of the cylindrical reshaped sample 7 with a diameter of 100mm and a height of 200mm, use a zs-100 drilling rig to drill a 130mm injection hole along the injection direction, drill a hole of 1 diameter 8mm and clear it cuttings;

Step S2, prepare the colloid: place the adhesives A and B on the front end of the electric heating fan, adjust the temperature of the electric fan to 80 degrees, and measure 1.1ml of the A glue and 1.1ml of the B glue respectively with a measuring cylinder, according to the A glue: Glue B is mixed with heating at a ratio of 1:1. Finally, measure 0.4ml of dodecyl to tetradecyl glycidyl ether and mix with 0.04ml of ethanol, and add it to the mixed glue AB to slow down the initial coagulation of the colloid. Time, increase the pouring time, and strengthen the sealing effect.

Step S3, treatment of the liquid injection pipe: use an O-type fluororubber sealing ring 6 to cover the liquid injection pipe 2 with an inner diameter of 2 mm, an outer diameter of 4 mm and a length of 75 mm at a distance of 5 mm from the bottom, and fix it with the liquid injection pipe 2. Choose and elastic The sealing tape 5 with the same thickness as the sealing ring 6 compresses the outside of the elastic sealing ring 6, so that the outermost tape 5 just forms a sealing gasket with a diameter of 8 mm.

Step S4, fix the liquid injection pipe: extend the liquid injection pipe 2 into the liquid injection hole 70mm and fix it, so that it is a certain distance from the bottom of the hole to meet the requirement that the open hole section 4 must be reserved for the hydraulic fracturing test.

Step S5, inject colloid and wait for cementation: choose a 5ml needle tube and a 2mm diameter needle, suck the prepared colloid, and insert the needle into the bottom of the annular cementation area 3 formed by the remodeling sample 7 and the injection tube, first inject 0.04ml of colloid, Then inject 8 times, each injection of 0.3ml, with a time interval of 10s, and ensure that the tip of the needle pierces the colloid each time until the colloid overflows the drill hole, remove the needle tube, and let the colloid and rock sample 7 form a polymer Shen area 3.

The hydraulic fracturing simulation test was carried out on the sealed sample, and the cross-sectional view of the fractured rock sample was observed, and it was found that in the sealing section, no fluid leakage occurred at the cemented interface between the liquid injection pipe 2 and the rock sample 7, but obvious cracks occurred in the fracturing target area. , as shown in Figure 3, it can be seen from the figure that the present invention has a better effect and a larger effective range of hydraulic fracturing. As shown in Figure 4, it can be seen from the water pressure curve that the change of water pressure in the fracture meets the requirements of the test, that is, it reaches the fracture initiation pressure of the rock sample and meets the requirements of hydraulic fracturing fluid injection pressure.

Example 2

Step S1 of the liquid injection pipe sealing method of the present invention is explained by the liquid injection pipe sealing of the cylindrical rock sample. Drilling: at the center of the upper surface of the cylindrical reshaped sample with a diameter of 100 mm and a height of 200 mm, use a zs-100 drilling rig along the Drill into the 130mm injection hole in the direction of injection, with a diameter of 11mm and remove the cuttings; Step S2, prepare colloid: put the adhesives A and B on the front of the electric heating fan, adjust the temperature of the electric fan to 80 degrees, and use Measure 2ml of Glue A and 2ml of Glue B in a graduated cylinder, mix them while heating according to the ratio of Glue A: Glue B at 1:1, and finally measure 0.55ml of dodecyl to tetradecyl glycidyl ether and 0.05ml mixed with ethanol, and added to the mixed AB glue to slow down the initial sticking time of the colloid, increase the pouring time, and strengthen the sealing effect.

Step S3, treatment of the liquid injection pipe: use an O-type fluororubber sealing ring to cover the liquid injection pipe with an inner diameter of 2 mm, an outer diameter of 4 mm and a length of 75 mm at a distance of 5 mm from the bottom, fix it with the liquid injection pipe with glue, and select the thickness of the sealing ring. The sealing tape of the same thickness compresses the outside of the sealing ring, so that the outermost tape just forms a sealing gasket with a diameter of 11 mm.

Step S4, fix the liquid injection pipe: extend the liquid injection pipe into the liquid injection hole 70mm and fix it so that it is at a certain distance from the bottom of the hole to meet the requirement that an open-hole section must be reserved for the hydraulic fracturing test.

Step S5, inject colloid and wait for cementation: select a 5ml needle tube and a 2mm diameter needle, suck the prepared colloid, put the needle into the bottom of the annular cementation area formed by the reshaped sample and the injection tube, first inject 0.08ml of colloid, and then divide 8 injections, each injection of 0.57ml, the time interval is 9s, and when injecting the liquid, make sure that the tip of the needle pierces the colloid each time until the colloid overflows the drill hole, remove the needle tube, and consolidate the colloid and the rock sample.

Example 3

The sealing method of the liquid injection pipe of the present invention is illustrated by the liquid injection pipe sealing of the cubic shale sample

Step S1. Drilling: at the center of the upper surface of the 300×300×300mm cube shale sample, use a zs-100 drilling rig to drill a 200mm liquid injection hole along the liquid injection direction, with a diameter of 20mm and remove debris;

Step S2, prepare the colloid: put the adhesives A and B on the front end of the electric heating fan, adjust the temperature of the electric fan to 80 degrees, and measure 12ml of A glue and 12ml of B glue with a measuring cylinder respectively, according to A glue:B glue Mix with heating at a ratio of 1:1, finally measure 2.5ml of dodecyl to tetradecyl glycidyl ether and mix with 0.6ml of ethanol, add it to the mixed AB glue, slow down the initial sticking time of the colloid, It increases the pouring time and strengthens the sealing effect.

Step S3, treatment of the liquid injection pipe: use an O-type fluororubber sealing ring to cover the liquid injection pipe with an inner diameter of 6mm, an outer diameter of 10mm and a length of 120mm at a distance of 5mm from the bottom, fix it with the liquid injection pipe with glue, and select the thickness of the sealing ring. The sealing tape of the same thickness compresses the outside of the sealing ring, so that the outermost tape just forms a sealing gasket with a diameter of 20mm.

Step S4, fix the liquid injection pipe: extend the liquid injection pipe into the liquid injection hole 115mm and fix it, so that it is at a certain distance from the bottom of the hole to meet the requirement that the open-hole section must be reserved for the hydraulic fracturing test.

Step S5, inject colloid and wait for cementation: choose a 30ml needle tube and a 2mm diameter needle, suck the prepared colloid, and insert the needle into the bottom of the annular cementation area formed by the shale sample and the liquid injection tube, first inject 0.5ml of colloid, and then divide the 9 injections, each injection of 3ml, with a time interval of 10s, and ensure that the tip of the needle pierces the colloid each time until the colloid overflows the hole, remove the needle tube, and consolidate the colloid and shale samples.

Claims (4)

1. A liquid injection pipe sealing method suitable for a hypotonic reservoir hydraulic fracturing simulation test is characterized by comprising the following steps:

step S1, drilling: at the liquid injection position, drilling a diversion hole along the liquid injection direction to reach 3/5-2/3 of the length of the sample, and removing chips;

step S2, preparing colloid: respectively measuring an A glue accounting for 40-45% of the total colloid volume and a B glue accounting for 40-45% of the total colloid volume according to the A glue: mixing the glue B in a ratio of 1:1, measuring dodecyl-tetradecyl glycidyl ether accounting for 9-17% of the total volume of the glue and ethanol accounting for 1-3% of the total volume of the glue, and adding the mixed glue B serving as a diluent into the mixed glue AB;

step S3, pour spout end portion processing: sleeving an elastic sealing ring at a position 5-10mm away from the bottom of the liquid injection pipe, pressing the outer part of the elastic sealing ring by using a sealing adhesive tape with the width equal to the thickness of the elastic sealing ring sleeve, and fixing the elastic sealing ring and the liquid injection pipe;

step S4, fixing the liquid injection pipe: the liquid injection pipe with the processed end part is extended into a position 1/2-2/3 of the depth of the drilled hole to be fixed, and an open hole section is reserved;

step S5, glue injection: the method comprises the steps of extending a glue injection needle tube into the bottom of an annular space of a sample and a liquid injection tube, firstly, preliminarily injecting a small amount of glue to a sealed end part to form an initial setting interface, then slowly injecting the glue in 8-10 layers, wherein the injection interval of each layer is 9-10s, the tip of a needle head is always positioned in the glue during injection, and after all injection is completed, the glue consolidation strength is reached within 24 hours.

2. The method for sealing the liquid injection pipe suitable for the hydraulic fracturing simulation test of the hypotonic reservoir as claimed in claim 1, wherein the method comprises the following steps: the volume of the diluent dodecyl to tetradecyl glycidyl ether participating in the curing reaction accounts for 10 to 15 percent of the total colloid volume.

3. The method for sealing the liquid injection pipe suitable for the hydraulic fracturing simulation test of the hypotonic reservoir as claimed in claim 1, wherein the method comprises the following steps: the elastic sealing ring is a fluororubber o-shaped ring and is tightly combined with the liquid injection pipe.

4. The method for sealing the liquid injection pipe suitable for the hydraulic fracturing simulation test of the hypotonic reservoir as claimed in claim 1, wherein the method comprises the following steps: the fixed position of elastic sealing ring apart from annotating liquid pipe bottom 5mm, annotate the length of liquid pipe bottom apart from drilling bottom be 1/3 of drilling depth.

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